LONDON: Andrew Strauss has told his England team they will have to prepare for their biggest challenge yet now they are a "hunted" side after rising to number one in the world Test rankings.

Test captain Strauss led hosts England to a 4-0 series rout of India earlier this year as the Ashes holders climbed to the summit of the five-day game.

But England's new-found status will come under threat when they face Pakistan in a three-match series in the United Arab Emirates starting in January.

"We recognise that the next 12-18 months will be the biggest test we've had yet as a group," said Strauss, speaking at Lord's on Thursday after the announcement of a 10-year deal for financial firm Investec to become the sponsor of England's home Tests.

"It's a different mindset being the hunted rather than the hunters," opening batsman Strauss, who plays for Lord's-based Middlesex, added. "We'll have to retain that desperate desire to improve if we want to stay on top.

"There are a lot of teams below us who want to knock us off our perch."

After the Pakistan series, England complete their off-season Test programme with a two-match contest in Sri Lanka.

Next year England are at home to an improving West Indies and South Africa, who recently tied 1-1 in an exciting two-Test series with Australia, in three and four match campaigns respectively.

"We've seen a resurgence in West Indies cricket in recent times, so that will be a challenge for us," said Strauss.

"Hopefully (English) early-season conditions will suit us more than them.

"And we all know about the qualities of South Africa, they've just finished an outstanding series against Australia.

Earlier Thursday, Australia fast bowler Ryan Harris said two-Test series were a waste of time.

"Two-Test series, personally in my point of view, are pointless," said Harris. "If it's 1-1 at the end of the series you walk away with an empty feeling. Three-Test series have to be a minimum, if not more."

Crowds for Tests in England, even before the start of the team's rise to the top of the standings, have generally held up well, with tickets for the first four days of most matches frequently selling out well in advance.

The International Cricket Council (ICC) have repeatedly insisted the five-day game remains the pinnacle of the sport.

However, the decision to delay the introduction of a world Test championship until 2017 -- it was due to start in two years' time -- for commercial reasons was seen as a blow to the standing of cricket's oldest international format in an era of numerous one-day and Twenty20 internationals.

"In a lot of ways in the past we've relied on Test cricket always being around," said Strauss.

"Now we must knock our heads together to evaluate what's the best way of marketing it and how to bring people to the game.

"The added context of a world Test championship or something similar is a good idea.

"I'm buoyed by what great support there is for the game in this country, but I'm also quite aware that in other parts of the world it's less so.

"We're in a fortunate position here but it's up to administrators all over the world to ensure they keep working on the product."

Both Investec and the England and Wales Cricket Board (ECB) have refused to publicly reveal the worth of their sponsorship deal, although estimates in the British press have ranged from £20-40 million.

Investec were previously a sponsor of England home rugby union Tests.

But their 12-year relationship with the Rugby Football Union (RFU) ended in August -- before England's shambolic World Cup campaign in New Zealand which has reportedly alarmed sponsors concerned by a series of lurid headlines regarding the squad's conduct.